Method of positioning line scanning rasters in a color television camera and devices suitable for carrying out this method

Abstract

When adjusting a color television camera a specific test pattern comprising dark and bright areas is used which is placed in the ambient light of a scene to be taken. By means of measuring locations in line scanning rasters the black level and the peak-white value in the test pattern signals are fixed at reference values. Thus the picture signals are given the nominal values matching the ambient light. Then other measuring locations are moved, by scanning raster displacement and/or scanning raster shaping, to bright-dark transitions in the image of the test pattern at which an intermediate reference value is provided. Absolute scanning raster positioning is carried out without being influenced by non-linearities, in contradistinction to the case when using a reference scanning raster.

What is claimed is: 
     
       1. A method of registering a plurality of color television scanning rasters comprising setting each of the video signals to first and second reference values corresponding to respective first and second measuring locations in respective dark and bright areas of a test pattern, deriving an adjustment signal having a third reference value from a third measuring location disposed at a first transition between said dark and bright areas, and displacing each of said rasters to the location of said transition using said adjustment signal. 
     
     
       2. A method as claimed in claim 1 wherein said deriving step comprises deriving said adjustment signal also from a fourth measuring location disposed at a second bright-dark transition at right angles with respect to said first transition. 
     
     
       3. A method as claimed in claim 2 wherein said deriving step comprises deriving said third measuring signal from a third measuring location having a plurality of measuring points aligned in the field scan direction. 
     
     
       4. A method as claimed in claim 2 wherein said deriving step comprises deriving said adjustment signal from a single point at said fourth location every two interlaced line scanning rasters. 
     
     
       5. A method as claimed in claim 1 wherein said deriving step comprises deriving said adjustment signal also from a fifth measuring location near an edge of the scanning raster. 
     
     
       6. A device for registering a plurality of television scanning rasters of a test pattern having dark and bright areas, said device comprising a comparison circuit having first input means for receiving the picture signals, second input means for receiving first, second and third reference values corresponding to first, second and third measuring locations in said areas and the transition therebetween respectively, and an output means for providing an adjustment signal in accordance with the difference between said first, second and third reference values and said picture signals at said measuring locations respectively; means coupled to said output means for setting the bright and dark areas in the picture signal with respect to the first and second reference values in accordance with said adjustment signal; means coupled to said output means for shifting the position of said raster with respect to said transition in accordance with said adjustment signal; and a control pulse source coupled to said comparison circuit. 
     
     
       7. Device as claimed in claim 6, wherein the control pulse source has a plurality of outputs at which simultaneous control signals are produced, said comparison circuit having a plurality of inputs coupled to said pulse source outputs and a plurality of output means for simultaneous supply of of a plurality of picture signals, which comparison circuit has adjustment units which have storage capabilities 
     
     
       8. Device as claimed in claim 7, wherein each adjustment unit comprises a signal comparison device having inputs to which the picture signal and the reference are applied and an output, a flip-flop having first input coupled to said signal comparison device output and a further input coupled for control to the control pulse source, an adding circuit having at least one input coupled to an output of said flip-flop, a register which comprises a store storing a binary number coupled to said adding circuit. 
     
     
       9. Device as claimed in claim 6 wherein the control pulse source comprises a line counting circuit having inputs to which line and field control signals are applied, a succeeding gate circuit coupled to said line counting circuit and having outputs, a pluralilty of gates having inputs coupled to said succeeding gate, a plurality of flip-flops provided with inputs to which the line control signal and signals obtained from the line control signal and being delayed and lengthened line control signals by means of a plurality of multivibrators are applied and outputs coupled to said gates. 
     
     
       10. Device as claimed in claim 6, further comprising switches which for control are coupled to the control pulse source and for sequential picture signal input and adjustment signal output are coupled to the comparison circuit. 
     
     
       11. Device as claimed in claim 6, further comprising a signal detector means having an input coupled to an output of the comparison circuit in order to detect voltage changes and an ouput coupled to said control pulse source.